Aperture, Shutter Speed, ISO

In an ideal situation you would use the aperture you want to use, the speed you want to use, and the ISO you want to use. So what is an ideal situation? Let’s say you want to photograph a vase on a table outside on a sunny day. The vase isn’t going to move, so you can use a slow shutter speed. There’s plenty of light, so you can use pretty much any aperture you want.

Let’s say you want a shallow depth of field, which means that the distance front to back that is sharp will be small. Everything outside of that depth of sharp focus will be blurry and out of focus – perfect for what you want. And with all that daylight you can use the lowest ISO, which is a good idea because the lower the ISO the less digital noise there will be in the image.

Now let’s suppose you want to photograph the vase being smashed with a hammer. Now you need to use a fast shutter speed. And it’s probably a good idea to have a bigger depth of field to catch all the shards of pottery that are flying all over the place, some further forward and some flying further back. So you have stopped down the aperture and increased the shutter speed – and suddenly you have hit the buffers.

Daylight is fading now and there isn’t going to be enough light entering the camera. So you increase the ISO, which makes the sensor react to less light, and put up with the increase in noise.

At the last moment you can’t find the hammer so you go back to taking photos of the vase, and to make it more interesting you put another object, an antique inkwell in front of the vase and you put flowers in the vase. Now you need to increase the depth of field to get everything in focus, and that means stopping down the lens to a smaller aperture.

But that means less light getting into the camera and you can either use a slower shutter speed to give more time for light to reach the sensor in the camera – or you can increase the ISO to make the camera more sensitive to light (and, noise).

A breeze springs up and now you have to use a faster shutter speed to freeze the movement. So now you really only have one option, which is to increase the ISO.

And that is how photographers have to work, thinking about what will work best for what they want to do.

Why It Is Bad To Underexpose In Low Light

rhino adult and child

I shot this on auto-ISO, which means that I let the camera determine the ISO while I shot at the shutter speed and aperture at which I wanted to shoot.

The ISO was 4,000 because the light was very low in the late afternoon into evening. Still, something went wrong because the RAW file is underexposed by almost two stops. Here is the default, uncorrected setting:


When the light is low, the camera is very unforgiving if the photo is underexposed. I am not sure what caused it to underexpose, maybe the settings hit the buffers and it couldn’t expose enough for the limits I had placed on shutter speed.

What I mean by unforgiving is that when I open up the exposure in Photoshop, there is a lot of grain in the photo. You can see it in the corrected version at the top, and more so in this crop.


So What Is A ‘Stop’?

A ‘stop’ is a halving or doubling (depending on which way you are going) of the light entering the camera compared to the value of the adjacent ‘f-stop’

The standard ‘f-stop’ settings run something like f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22

And if you photograph, you may well have a lens with a maximum aperture of f1.8, which is a half-stop position.

So, for example, f2.8 lets in twice of much light as shooting with the same shutter speed and ISO at f4.

That’s why professional photographers use lenses that have wide maximum apertures such as f 2.8 or even f2.0 or f1.4. That gives them more freedom to use a lower ISO and/or a faster shutter speed.

The ‘problem’ with lenses with fast apertures, especially long focal length lenses is that there is more glass of greater diameter in them – and glass is heavy. Here for comparison are the weights of a couple of 300mm lenses. Of course, the f2.8 lens has more light-gathering power, but at the cost of size and weight.

AF-S NIKKOR 300mm f4E PF ED VR 755g (26 ounces)

AF-S NIKKOR 300mm f2.8 G ED VR II 2,900g (102 ounces)